Lightning Distance Calculator

This calculator requires the use of Javascript enabled and capable browsers. This calculator is designed to give the approximate distance from lightning, based on the speed of sound. Upon viewing a flash of lightning in the sky, count the number of seconds until you hear thunder. The formula is to divide the number of seconds by the speed of sound in feet per second. The delay between when you see lightning and when you hear thunder occurs because sound travels much, much slower than light. Sound travels through air at about 1100 to 1200 feet per second (our default is 1150). That is a little more than one mile per five seconds. This approximation will give you a good idea of how far away the lightning was. So, for example, if you counted 30 seconds between the lightning and the thunder, you can estimate that the lightning was about 6 miles away, since 30 divided by 5 = 6.

Enter the number of seconds from the flash of lightning until you hear the start of the thunder rumble. If you wish, you can adjust the speed of sound to your preferences; however, under most situations, our default should be used. You should not deviate above 1200 or below 1100 feet per second. When you have made your entries, click on Calculate. The distance is returned in miles. Use extreme caution and care around lightning!